bed, or at least restricted in its geographical extent, and is the result of an accumulation of drift-wood in an estuary of the cretaceous sea.

I am informed that it is seen over on the Elkhorn river about 35 miles west of this point.

Mr. Clark tells me that he dug twelve or fifteen feet below this bed and struck another seam of coal much better than the one cropping out. The lower bed must be the one in the Dakota group. Lithologically it is impossible to draw a line of demarcation between these formations here. Number 1 passes so imperceptibly into number 2, and number 2 into number 3, that there is no break, and yet their principal characteristics are very distinct. The first is a sandstone; second, a black plastic clay; third, a chalky limestone; and yet I cannot tell the exact point where one commences and the other ends.

The impressions of leaves have ceased to appear before the close of the Dakota group. The sandstones of the Dakota group occupy the whole country along the Platte from the mouth of the Elkhorn to a point some twenty miles beyond the entrance of the Loup fork. The intermediate counties between the Missouri and Platte have very few exposures of rock of any kind, so that quarries in this region, even though the rock is of inferior quality, are much prized.

The tertiary beds which make their appearance along the greater portion of the Niobrara, and really occupy a very large portion of western Nebraska, do not furnish much good building-stone. In order that the general geology of all this region may be better understood, I will give a general section of the cretaceous and tertiary rocks of the Missouri valley, which was first published by Mr. Meek and myself in the proceedings of the Academy of Sciences at Philadelphia. I have made such changes as the present state of our knowledge of this region requires, which are not of great importance.

The accompanying profile, also, along the Missouri river, from Fort Benton to the southern line of Nebraska, will show the basin-like character of the geological formations, and especially the subdivisions of the cretaceous rocks, and their relations to the tertiary.

Eq. Upper or white chalk and Maestricht beds. (Senonien, D'Orbigny.)

400 feet.

800 feet.

200 feet.

(Turonien and cenomanien of D'Orbigny.) Eq. Lower or gray chalk (and upper G. sand) of British geologists.

DAKOTA GROUP.

Although we have hitherto regarded this as a distinct group of cretaceous rocks, with a strong physical line of separation from the group above, I now think the evidence is clear that it passes imperceptibly in its lithological relations up into the Fort Benton group, without any break in time.

In the hills back of Dakota City there are repeated exposures which show the transition layers between the two sandstones of the one and the dark plastic clays of the other. The fossils, however, so far as we now know, are distinct, and for the practical purpose of investigating this rock they may be regarded as distinct groups.

We have referred the rocks of the Dakota group to the cretaceous epoch, from the fact that they have yielded numerous species of dicotyledonous leaves. Among these leaves, Dr. Newberry and Professor Heer have identified those of trees belonging to the genera Populus, (poplar,) Salix, (willow,) Alnus, (alder,) Platanus, (sycamore,) Liriodendron, (tulip,) Ficus, (fig,) and many others. In the history of geology, no dicotyledonous leaves have been found in fossil condition in rocks older than the cretaceous era. As they are found here in beds lying underneath rocks containing well-known cretaceous fossils, their age is beyond a doubt.

The discovery of these vegetable impressions in sandstones of the cretaceous period at this locality has afforded to geologists an instructive lesson. A geologist of high character, and one of the best botanists in Europe, Professor Heer, declared these plants to be of tertiary age, and even identified some of them with plants already known in the Old World in tertiary rocks.

In 1863, Professor Capellini, of the University of Bologna, Italy, and Professor Marcou, of Switzerland, made a journey up the Missouri river to study these rocks, and to settle this vexed question.

The results of their labors were published in the French and Swiss geological journals. The article of Professor Capellini was first translated by me in this country for Silliman's Journal.

Professor Capellini, in a short but very interesting article, confines his observations mostly to the rocks of the Dakota group, and remarks that he does not hesitate to regard the observations of American geologists as entirely just; the following remarks close the article of Professor C:

"After all we have observed in relation to the environs of Sioux City, it is easily seen that a stratigraphic series, so complete, throws a clear light upon the isolated facts first noticed at Tekamah and Blackbird Hill, and indicates the exact position of the rocks with dicotyledonous leaves, analogous to the tertiary leaves of Europe, but belonging in reality to the chalk.

"It may be estimated that the thickness of these cretaceous strata in the environs of Sioux City is about forty metres. They may be divided into two distinct parts, one rich in leaves, a fresh water formation; the other truly chalky, with fishes and inoceramus of marine origin. Both are probably not older than the chalk of Maestricht.

"This has been my opinion from the time I admitted that the dicotyledonous leaves of the Big Sioux and Tekamah were cretaceous.

"Once the age of the Mollasse with leaves established by the aid of the stratigraphy and the animal fossils, it would be interesting if it were possible to arrive at the same results by the vegetable remains. On this account Professor Heer came to my aid and investigated the specimens 1 collected in my explorations. More than a dozen species were recognized among the leaves from Tekamah, Blackbird Hill and Big Sioux, but it was especially the first locality which furnished the best specimens.

"We are convinced that when observations are exact and determinations

made from careful examination of specimens, there is never any disagreement between stratigraphical and paleontological laws."

The remarks of Professor Heer, which preface his descriptions of the fossil plants by Professor Capellini, are so interesting and important that we copy them entire.

"The collection of Mr. Capellini contains sixteen species; four are badly preserved, twelve are determinable; nevertheless, of the latter several are but fragments, so that their determination is difficult and not sufficiently positive. This is especially the case with Phyllites, which I have referred to the genera Platanus and Andromeda.

It is certain that all the leaves found by Mr. Capellini are dicotyledonous, and with great probability one may be referred to the genus Ficus, one to Salix, one to Diospyrus, two to Populus, and two to Magnolia, although there are no accompanying fruits or other parts to confirm these determinations. These genera are yet living, and they are also found in the tertiary formations.

If we compare these plants of Nebraska with the cretaceous plants of Europe, we find no identical species among them. I sent drawings of them to Dr. Debey, of Aix-la-Chapelle, who discovered in that locality a cretaceous flora. He has written to me that he has not found one species identical. Even the greater part of the genera are different. There is but one Cissite, (.C aceroides, Debey,) which recalls slightly the C. insignis. (Plate 4, Fig. 5.) The cretaceous plants of Henant, Belgium, those of Blankenburg and Quedlinburg, are also very different.

Professor Schenck has recently sent to me a collection of plants of Quedlinburg for determination. Besides conifers and fern characteristic of the chalk, it contains dicotyledonous leaves, but no forms like those of Nebraska. The cretaceous flora of Moletein, Moravia, which I have lately studied, exhibits more resemblance. It contains two species of Ficus, which much resemble the Ficus of Nebraska, two superb species of Magnolia, one with a fruit cone.

There is a relationship between the flora of Nebraska and that of the upper chalk of Europe, although identical species are wanting. But to the present time no characteristic genus of the cretaceous flora of Europe has been found in Nebraska.

If we compare the plants of Nebraska with the tertiary plants we find no identical species, but seven genera (Populus, Salix, Ficus, Platanus, Andromeda, Diospyrus, and Magnolia) are miocene, and likewise living.

It then appears that the Nebraska flora is related more to the tertiary than to the cretaceous flora of Europe, a fact which struck me when I first saw drawings of the former. But it should be remarked that we know but a very small number of American species, and on the other hand the European cretaceous flora has more relationship with tertiary flora than I at first supposed. I have found in the cretaceous flora of Moletein, Moravia, species of Ficus and Magnolia which resemble tertiary species; a Myrtacea, which is a near neighbor to the Ucalyhtus rhododendroides, (Mass.) of Mt. Bolca, a Juglans and a Laurinea, which also have their analogues in the tertiary flora; a Pinus and two other conifers which belong to the genus Sequoia, which was extensively distributed in Europe and America in the miocene epoch, and which is now only found in California.

As the cretaceous fishes are more nearly related to the tertiary than to the jurassic fishes, the upper cretaceous flora is also entirely different from the jurassic and more nearly allied to the tertiary floras, and it appears that in America the relation between the tertiary and cretaceous flora is yet more intimate than in Europe.

It is remarkable that the plants of Nebraska (as Magnolia and Liriodendron) present relations with the existing flora of America, whilst the cretaceous flora of Europe has more of an Indo-Australian character. It thus appears that since

the cretaceous epoch the American flora has not undergone a change so great as the European flora. While the cretaceous flora of Europe is entirely different from the existing European flora, that of Nebraska contains eight genera yet found in America, and it is the more remarkable that the greater part are yet found in a country under the same latitude."

Professor Heer describes the following species of plants from this group in this memoir:

Populus litigiosa, (?) Debeyana, Salix nervillosa, Betulites denticulata, Ficus primordialis, Platanus, (?) Newberryana, Proteoides grevilleaformis, P. daphnegenoides, P. acuta, Aristolochites dentata, Andromeda parlatorii, Diospyrus primaevus, Cissites insignis, Magnolia alternans, M. Capellini, Liriodendron meekia, Phyllites vanona.

One instructive lesson is derived from the mistakes of these eminent men, that in the progress of geological development, America was almost or quite one epoch ahead of Europe that the fauna and flora of the cretaceous period in this country was really more nearly allied to those of the tertiary period in Europe, and that, geologically speaking, America should be called the Old World and Europe the New. This point will be again alluded to in our remarks on the tertiary rocks. Again, there is evident simplicity in the form and ornamentation of these leaves, which marks the dawn of the appearance on this planet of trees like our forest, fruit, and ornamental trees.

The beauty of foliage in our present dicotyledonous trees is largely due to the serrations and various forms and patterns which they present, but, so far as my observations have extended, the reverse is the case with this cretaceous vegetation for the most part-thus slowly progressing through the tertiary period from simplicity up to greater complexity and beauty.

The question would arise naturally, have any remains of land animals been found in this group mingled with these vegetable impressions? None have yet been observed along the Missouri at this locality, and as they have now been studied with considerable care, we may never find any. That land animals did exist we cannot doubt, for the forests which furnished these leaves could not have existed far away.

The leaves are so perfect that they could not have been transported to a great distance before they were imbedded in the sand. On the eastern slope of the Big Horn mountains there are a series of beds which hold a position between the jurassic beds and the Fort Benton group, which I have referred to the Dakota group.

Here occur beds of impure earthy lignite, large quantities of silicified wood and uncharacteristic bones, which Dr. Leidy thinks belonged to some huge saurian. No remains of strictly land animals have ever been found.

The geographical extension of this group of rocks outside of this State has been found to be very extensive. The belt of country occupied by them in Nebraska runs nearly southeast and northwest, and is from 60 to 80 miles wide, extending far south into New Mexico, and possibly further and northward into Iowa and Minnesota, and probably far up into British America. It is believed also to occur all along the Rocky mountains, although as yet no positive proof from fossils has been obtained.

There are a series of beds between well-known cretaceous and jurassic rocks in those regions, which have been regarded as belonging to the Dakota group; also, near the sources of the Missouri are a series of beds differing from any other yet described, containing many species of shells and a bed of lignite, which seems to belong to this group. These latter beds need more careful study before the position can be positively fixed in this section.

Along the Atlantic coast, especially in New Jersey, the lower cretaceous beds seem to be lithologically similar, in containing numerous dicotyledonous leaves, so that it is now regarded as the equivalent of the Dakota group of the west.